Determination of calcium was studied by a coprecipitation method with a strontium carbonate andthe subsequent atomic absorption spectrometry (AAS).
Fifteen milliliters of 2 g Sr/l strontium chloride and 15 ml of 20 w/v 70 potassium carbonate wereadded to sample water, which was then stirred for 30 min. After collecting the precipitate containingcalcium on a membrane filter, the precipitate was dissolved with 2 ml of (1+12) HNO₃, andwas used for AAS. The linear range of calibration curve was from 10 to 1,000 μg/l, and the limitof detection and the lower limit of determination were found to be 1.5 and 5.1 μg/l, respectively.This method was not influenced by sample size from 100 to 1,000 ml, and was satisfactorily appliedto determine calcium ions in environmental water without any interfering effects of the copresentions.
The values obtained from the calibration curve method agreed with those from the standard addition method.

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For the net power generation by the salinity concentration difference between sea and river waterusing the PRO system, the optimum feed ratio was obtained for the pressurized sea water type.The hollow fiber permeator was partitioned to get the minimum surface velocity for realizing thesalinity power generation. The relations among partition number, shell size, and bulk velocity ofsea water were introduced by using both the osmotic transport equations considering the internalpolarization in the membrane and equations for shell size, structure, and pressure loss.
Cylindrical 5130-type permeator of hollow fibers, of which the sea water passage is partitionedinto four, is selected for tests in laboratory. Experiments of sham power generation test show thatthe maximum power was obtained at the feed ratio near the designed point. This is due to theeffectiveness of the partition and the small pressure drop in the permeator.
In future it is important to develop the system of a large feed ratio and to develop the membrane of small internal polarization for a larger permeator.

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A new coprecipitation method for the fluorometry of selenium (IV) in sea water has been developed.Selenium (IV) was coprecipitated with thorium (IV) hydroxide from 1,000 ml of sea water at pH 7.0.Without aging, the precipitate was centrifuged and then dissolved in hydrochloric acid. Selenium (IV) with the thorium was determined by the usual fluorometry with 2, 3-diaminonaphthalene, because theinterfering thorium (IV) ions were masked by EDTA and sodium fluoride. This method was applicableto groundwater samples. The concentrations of selenium (IV) in coastal sea water and groundwater were in the range of 21.6-23.7 ng/l and 39.5-54.4 ng/l, respectively.

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[in Japanese]

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